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These passes were buggy, MIR building is now responsible for
canonicalizing `ConstantIndex` projections and `MoveData` is responsible
for splitting `Subslice` projections.
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* `min_length` is now exact for const index elements.
* const index elements are always from the start.
* make array `Subslice` `PlaceElems` count both `from` and `to` from the
start.
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Index impl, remove body fn
rustc_codegen_ssa: Fix BodyAndCache reborrow to Body and change instances of body() call to derefence
rustc_mir: Fix BodyAndCache reborrow to Body and change intances of body() call to derefence
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rename all body_cache back to body
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(lifetime errors still exist)
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(ReadOnly)BodyCache type errors
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invalidate cache when accessing unique terminator
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This prepares the code base for when projection is interned. Place's
projection field is going to be `&List<PlaceElem<'tcx>>` so we won't be
able to pattern match against it.
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Return `false` from `needs_drop` for all zero-sized arrays.
Resolves #65348.
This changes the result of the `needs_drop` query from `true` to `false` for types such as `[Box<i32>; 0]`. I believe this change to be sound because a zero-sized array can never actually hold a value. This is an elegant way of resolving #65348 and #64945, but obviously it has much broader implications.
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Instead just use `pprust::path_to_string(..)` where needed.
This has two benefits:
a) The AST definition is now independent of printing it.
(Therefore we get closer to extracting a data-crate.)
b) Debugging should be easier as program flow is clearer.
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Make `into` schedule drop for the destination
closes #47949
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Don't mark borrows of zero-sized arrays as indirectly mutable
Resolves #64945
r? @oli-obk
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Now the first row of each basic block is always light instead of
changing seemingly at random.
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This adds a dataflow analysis that determines if a reference to a given
`Local` or part of a `Local` that would allow mutation exists before a
point in the CFG. If no such reference exists, we know for sure that
that `Local` cannot have been mutated via an indirect assignment or
function call.
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The non-global context was removed; there's only one context now. This
is a noop method that only serves to confuse readers -- remove it.
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A more generic interface for dataflow analysis
#64470 requires a transfer function that is slightly more complex than the typical `gen`/`kill` one. Namely, it must copy state bits between locals when assignments occur (see #62547 for an attempt to make this fit into the existing framework). This PR contains a dataflow interface that allows for arbitrary transfer functions. The trade-off is efficiency: we can no longer coalesce transfer functions for blocks and must visit each statement individually while iterating to fixpoint.
Another issue is that poorly behaved transfer functions can result in an analysis that fails to converge. `gen`/`kill` sets do not have this problem. I believe that, in order to guarantee convergence, flipping a bit from `false` to `true` in the entry set cannot cause an output bit to go from `true` to `false` (negate all preceding booleans when `true` is the bottom value). Perhaps someone with a more formal background can confirm and we can add a section to the docs?
This approach is not maximally generic: it still requires that the lattice used for analysis is the powerset of values of `Analysis::Idx` for the `mir::Body` of interest. This can be done at a later date. Also, this is the bare minimum to get #64470 working. I've not adapted the existing debug framework to work with the new analysis, so there are no `rustc_peek` tests either. I'm planning to do this after #64470 is merged.
Finally, my ultimate plan is to make the existing, `gen`/`kill`-based `BitDenotation` a special case of `generic::Analysis`. Currently they share a ton of code. I should be able to do this without changing any implementers of `BitDenotation`. Something like:
```rust
struct GenKillAnalysis<A: BitDenotation> {
trans_for_block: IndexVec<BasicBlock, GenKillSet<A::Idx>>,
analysis: A,
}
impl<A> generic::Analysis for GenKillAnalysis<A> {
// specializations of `apply_{partial,whole}_block_effect`...
}
```
r? @pnkfelix
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Replace `state_for_location` with `DataflowResultsCursor`
These are two different ways of getting the same data from the result of a dataflow analysis. However, `state_for_location` goes quadratic if you try to call it for every statement in the body.
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Make rustc_mir::dataflow module pub (for clippy)
I'm working on fixing false-positives of a MIR-based clippy lint (https://github.com/rust-lang/rust-clippy/pull/4509), and in need of the dataflow infrastructure.
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This can be removed once dataflow-based const validation is merged.
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